Optical bench on substrate and method of making the same

ABSTRACT

An optical bench including a substrate having a trench with the trench having an angled sidewall on which a reflective coating is provided. The optical bench also includes a first device and a waveguide positioned within the trench, a second device optically connected to the first device, and at least one active circuit electrically connected to the first device with the waveguide being positioned optically between the first device and the reflective coating. The optical bench also includes an optically transparent material that forms a first interface with the first device and a second interface with a first surface of the waveguide.

PRIORITY CLAIM

The present application is a continuation of U.S. application Ser. No.14/699,151, filed Apr. 29, 2015, which was a continuation-in-part ofU.S. application Ser. No. 13/403,566, filed Feb. 23, 2012, both of whichare incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present disclosure relates generally to an integrated circuit.

BACKGROUND

A multi-chip module package (MCM) integrates chips with differentfunctions and made of different processes. Some MCMs utilize substratematerials based on ceramic or organic polymers, which, in certainconfigurations, may have insufficient coefficient of thermal expansion(CTE) matching to semiconductor chips and/or heat dissipation property.This causes potential reliability issues for III-V semiconductormaterial based optoelectronic chips and/or high power amplifiers.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is now made to the following descriptions taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a cross-sectional diagram of an optical bench on substrateaccording to some embodiments;

FIGS. 2A-2E are cross-sectional diagrams of various steps of fabricationprocess of the optical bench on substrate in FIG. 1 according to someembodiments;

FIGS. 3A-3C are cross-sectional diagrams of various steps of anotherfabrication process of the optical bench on substrate in FIG. 1according to some embodiments; and

FIG. 4 is a cross-sectional diagram of an optical bench on a substrateaccording to some embodiments.

DETAILED DESCRIPTION

The making and using of various embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use, and do notlimit the scope of the disclosure.

In addition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.Moreover, the formation of a feature on, connected to, and/or coupled toanother feature in the present disclosure that follows may includeembodiments in which the features are formed in direct contact, and mayalso include embodiments in which additional features may be formedinterposing the features, such that the features may not be in directcontact. In addition, spatially relative terms, for example, “lower,”“upper,” “horizontal,” “vertical,” “above,” “below,” “up,” “down,”“top,” “bottom,” etc. as well as derivatives thereof (e.g.,“horizontally,” “downwardly,” “upwardly,” etc.) are used for ease of thepresent disclosure of one features relationship to another feature. Thespatially relative terms are intended to cover different orientations ofthe device including the features.

FIG. 1 is a schematic diagram of an optical bench 100 on substrateaccording to some embodiments. The optical bench 100 includes a laserdiode land a photo diode 2 mounted on a substrate 3. The laser diode 1and the photo diode 2 comprise III-V semiconductor materials and operateon electromagnetic wavelengths in the range of 450 nm-1700 nm in someembodiments. The substrate 3 comprises any suitable material, such assilicon. An etching hard mask 4 comprises SiN or SiO₂ and is able toachieve at least 30 μm etch depth in some embodiments. The etching hardmask layer 4 over the area for a trench 21 and/or an optical waveguide19 is removed. In some examples, the etching hard mask layer 4 comprisesSiN of at least 30 nm in thickness. In further examples, the etchinghard mask layer 4 comprises SiO₂ of at least 100 nm in thickness. Areflector layer 5 comprises at least one of Cu, Al, Ag, or Au,multi-layered dielectrics, or any other suitable material having areflective property at desired electromagnetic wavelengths. In someembodiments, the reflector layer 5 has at least 90% reflectivity atselected wavelengths. In some embodiments, a material of reflector layer5 is chosen to selectively reflect a desired waveband and to eitherabsorb or transmit wavelengths outside the desired waveband.

A dielectric layer 6 comprises SiO₂ or other low-k dielectric materialssuch as porous SiO₂, organic polymers such as polymide orPolybenzobisoxazole (PBO), or hybrid-organic polymers such aspolysiloxane in some embodiments. To achieve high performance at radiofrequency (RF) and microwave frequency, the thickness of the dielectriclayer 6 is at least 300 nm where substrate 3 is a high resistancesilicon substrate (resistivity >3000 ohm-cm) in some embodiments. Thethickness of the dielectric layer 6 is at least 1 μm where substrate 3is part of normal resistance wafers (resistivity is from 1 ohm-cm to 10ohm-cm) in some embodiments.

A redistribution layer (RDL) 7 over the substrate 3 is an electricallyconductive layer on a chip that allows the Input Output (TO) pads of anintegrated circuit available in other locations. The RDL 7 comprises Al,Cu, or any other suitable electrically conductive material, and has morethan 1 μm thickness for high speed applications over 2 Gbps in someembodiments. A passivation layer 8 comprises SiO₂, SiON, SiN,multi-stacks of these materials, or any other suitable materials in someembodiments. The thickness of the passivation layer 8 is from about 200nm to about 800 nm for pad protection in some embodiments.

A bottom cladding layer 9 comprises SiO₂/SiON in some embodiments.Bottom cladding layer 9 is formed by plasma-enhanced chemical vapordeposition (PECVD) in some embodiments. In some embodiments, spin-ondielectrics or polymers are used to form the bottom cladding layer 9.The thickness of the bottom cladding layer 9 is at least 500 nm in someembodiments to prevent optical leakage. A core layer 10 comprisesSiON/SiN in some embodiments. Core layer 10 is formed by plasma-enhancedchemical vapor deposition (PECVD) in some embodiments. In someembodiments, spin-on dielectrics or polymers are used to form the corelayer 10. The thickness of the core layer 10 is at least 15 μm in someembodiments. A top cladding layer 11 comprises SiO₂/SiON in someembodiments. Top cladding layer 11 is formed by plasma-enhanced chemicalvapor deposition (PECVD) in some embodiments. In some embodiments,spin-on dielectrics or polymers are used to form the top cladding layer11. The thickness of the top cladding layer 11 is at least 500 nm insome embodiments to prevent optical leak. In some embodiment, an opticalfiber can be placed in the trench 21 as the waveguide 19.

The bottom cladding layer 9, the core layer 10, and the top claddinglayers 11 form the waveguide 19 inside a trench 21 as an optical linkmedium for the electromagnetic wavelengths used by the laser diode 1and/or the photo diode 2. The refractive index of the core layer 10 ishigher than that of the bottom and top cladding layers 9 and 11, and therefractive index difference is at least 0.02 in some embodiments toprevent optical leakage. In at least one example, three polymer layersfor the bottom cladding layer 9, the core layer 10, and the top claddinglayer 11 are deposited by a spin on process, and then a lithographyprocess is used to define dimensions of the optical waveguide 19. Anoptical path 20 is an exemplary light path of light (electromagneticwave) emitted from the laser diode 1, reflected by first a sloping sideof the reflector layer 5, through the optical waveguide 19, reflected bya second sloping side of the reflector layer 5, then to the photo diode2.

An under-bump metallization (UBM) layer 12 comprises any suitableunder-bump metallurgy, e.g., Cu/Ni, in some embodiments. A bump layer 13comprises lead-free solder or gold bumps in some embodiments. In someembodiments, bump layer 13 comprises a copper pillar. The bump layer 13comprises micro bumps for flip-chip bonding with semiconductor-basedoptical and electrical chip in some embodiments. The overall thicknessfor the UBM layer 12 and the bump layer 13 is from about 1 μm to about15 μm in some embodiments. Through substrate vias (TSVs) 14 formedthrough the substrate 3 comprises Cu or any other suitable electricallyconductive materials in some embodiments. The TSVs 14 are used toprovide backside electrical connections, and are fabricated using anysuitable methods and materials known in the art.

Another dielectric layer 15 comprises SiO₂ or other low-k dielectricmaterial such as porous SiO2, organic polymers such as polymide orPolybenzobisoxazole (PBO), or hybrid-organic polymers such aspolysiloxane in some embodiments. To achieve high performance at radiofrequency (RF) and microwave frequency, a thickness of the dielectriclayer 15 is at least 300 nm where substrate 3 is a high resistancesilicon substrate (resistivity >3000 ohm-cm) in some embodiments. Thethickness of dielectric layer 15 is at least 1 μm where substrate 3 ispart of normal resistance wafers (resistivity is from 1 ohm-cm to 10ohm-cm) in some embodiments. A backside redistribution layer (RDL) 16comprises Al, Cu, or any other suitable electrically conductivematerial, and has more than 1 μm thickness for high speed applicationsover 2 Gbps in some embodiments.

The trench 21 has sloping sides with a slope angle θ ranging from about42° to about 48° with respect to a top surface of substrate 3 and has adepth of more than 30 μm in some embodiments to accommodate the opticalbeam from the laser diode 1, e.g., a vertical cavity surface emittinglaser (VCSEL). In some embodiments, laser diode 1 has a beam diversionangle of about 20°-30° with a beam size of about 10 μm to about 15 μm.

The integrated optical bench 100 on substrate facilitates coupling thelight from the laser diode 1 to the reflector layer 5 and into thewaveguide 19. The integrated optical ben 100 also leads the light out ofwaveguide 19 to the reflector layer 5 to be received by the detectordiode 2. The optical bench 100 on substrate is implemented with oneportion on either side of the line 22 in some embodiments. For example,in one or more embodiments, the optical bench 100 includes thetransmitting portion on the left side of the line 22 and having thelaser diode 1 as a transmitter. In one or more embodiments, the opticalbench 100 includes the receiving portion on the right side of the line22 and having the photo diode 2 as a receiver. The large waveguide 19dimension (greater than 15 μm in some embodiments) also allows light tobe coupled into and out of optical fibers for out-of-chip communicationwith separate chips of a semiconductor device.

The optical bench 100 on substrate structure can provide bettercoefficient of thermal expansion (CTE) matching and/or heat dissipationfor optical components such as the laser diode 1 and the photo diode 2mounted on the substrate 3 when the substrate 3 comprises semiconductormaterials such as silicon, compared to other substrate or interposermaterials such as ceramic or organic polymer. More robust and costefficient integration of optics using silicon micro-fabricationtechnology is achieved by the optical bench 100 on substrate compared tosome other assembly using discrete optical components. Also, there isless crosstalk among optical channels by using the optical waveguide 19to help secure data transfer.

Furthermore, by configuring the optical bench 100 as a transmittingportion (e.g., the portion on the left side of the line 22 and havingthe laser diode 1 as a transmitter), or as a receiving portion (e.g.,the portion on the right side of the line 22 and having the photo diode2 as a receiver), inclusion of an optical input/output off the packageis possible. This optical bench 100 on substrate platform offers higherdata rate transfers inside the package than typical electricalconnections by integrating optical components and optical options forsignal input and output.

FIGS. 2A-2E are schematic diagrams of various steps of fabricationprocess of the optical bench on substrate in FIG. 1 according to someembodiments. In FIG. 2A, the RDL 7 is formed over the dielectric layer6, e.g., by physical vapor deposition (PVD), for metal routing and metaltraces for high speed electrical signal propagation. The passivationlayer 8 (e.g., silicon nitride or oxide) is deposited afterward formetal protection, e.g., by chemical vapor deposition (CVD). Thepassivation layer 8, the dielectric layer 6, and the etching hard mask4, e.g., silicon nitride or silicon oxide, are removed from an areawhere the trench 21 is to be formed.

In FIG. 2B, the trench 21 (at least 30 μm deep in some embodiments),including the sloping sides with a slope angle θ, is fabricated by wetetching using KOH(aq)/IPA or TMAH solution. One method to control theanisotropic wet etching is achieved by using KOH (25 wt %-35 wt %) withno less than 5 wt % IPA quantity. The temperature is kept at about 60°C.-70° C. during the wet etching to achieve a reasonable etch rate of0.2-0.6 microns per minute during the wet etching and to preventexcessive hillock formation.

The reflector layer 5 having sloping sides with a slope angle θ (e.g.,42°-48°) is formed on the trench 21. This step may include depositing anadhesion dielectric layer, then a barrier/adhesion metal layer, such asTi or Cr, and finally a highly reflective metal such as Al, Cu, Ag, orAu with a thickness greater than 50 nm to achieve reflectivity greaterthan 90% in some embodiments. The deposition process is performed byphysical vapor deposition (PVD) or electroplating, in at least oneexample. Any other suitable reflective material or process is alsousable.

In FIG. 2C, the waveguide 19, e.g., polymer, for the optical path insidethe trench 21 is formed. This step includes forming the bottom claddinglayer 9 (e.g., dielectric or polymer) by chemical vapor deposition (CVD)or a coater (for dielectric or polymer), then the core layer 10 (e.g.,polymer), and the top-cladding layer 11 (e.g., dielectric or polymer) insome embodiments. The waveguide 19 can be defined by etching andunnecessary portions of the reflector layer 5 are removed in someembodiments. In some embodiments, a portion of an optical fiber isplaced in the trench 21 as the waveguide 19.

In FIG. 2D, the UBM layer 12 such as Cu/Ni is formed, e.g., byevaporation or sputtering, or by chemically plating. A bump layer 13 isformed or placed on the UBM layer 12 in many ways, includingevaporation, electroplating, printing, jetting, stud bumping, and directplacement.

In FIG. 2E, the laser diode 1 and the photo diode 2, as well as otherdriver or transimpedance amplifier (TIA) chips, are flip-chip mounted(and/or wire-bonded as necessary) over the substrate 3. In FIG. 2E, theportion on the left side of the line 22 is the transmitting portion ofthe optical bench shown in FIGS. 2A-2D, and the portion on the rightside of the line 22 is a receiving portion that can be fabricated in thesame or similar process flow described with respect to FIGS. 2A-2D.

FIGS. 3A-3C are schematic diagrams of various steps of anotherfabrication process of the optical bench on substrate in FIG. 1according to some embodiments. In FIG. 3A, the etching hard mask 4 andthe dielectric layer 6 are formed over the substrate 3. The etching hardmask 4, e.g., silicon nitride or silicon oxide, and the dielectric layer6 are removed from an area where the trench 21 is to be formed.

In FIG. 3B, the trench 21 with the slope angle θ (as shown in FIG. 1) isformed by etching, e.g., using KOH(aq)/IPA or TMAH solution. One methodto control the anisotropic wet etching is achieved by using KOH (25 wt%-35 wt %) with no less than 5 wt % IPA quantity. The temperature iskept at about 60° C.-70° C. during the wet etching to achieve areasonable etch rate of 0.2-0.6 microns per minute during the wetetching and to prevent excessive hillock formation.

The reflector layer 5 having a slope angle θ (e.g., 42°-48°) is formedon the sloping side of the trench 21. This step may include depositingan adhesion dielectric layer, then a barrier/adhesion metal layer, suchas Ti or Cr, and finally a highly reflective metal such as Al, Cu, Ag,or Au with a thickness greater than 50 nm to achieve reflectivitygreater than 90% in some embodiments. The deposition process isperformed by physical vapor deposition (PVD) or electroplating, in atleast one example. Any other suitable reflective material or process isusable. The reflector layer 5 is removed in areas where it is notnecessary by a lithography process in some embodiments.

In FIG. 3C, the RDL 7 is formed and defined for metal routing and metaltraces for high speed electrical signal propagation. Additionaldielectric layer for electrical isolation and microwave confinement canbe formed as necessary. After the step in FIG. 3C, the process flow canproceed to the operation of forming the passivation layer 8 (e.g.,silicon nitride or oxide) for metal protection as described with respectto FIG. 2A, and then proceed to the steps described in FIGS. 2C-2Eafterwards.

FIG. 4 is a cross-sectional diagram of an optical bench 400 on asubstrate according to some embodiments. Optical bench 400 includessimilar elements as optical bench 100. Same elements have a samereference number. In comparison with optical bench 100, optical bench400 includes laser diode 1 within trench 21. In some embodiments, laserdiode 1 is called a light emitting device. RDL 7 electrically connectslaser diode 1 to an active circuit 410. Active circuit 410 is configuredto generate a signal to provide information to laser diode 1 foremitting light to be received by photodetector 2. In some embodiments,photodetector 2 is called a light receiving device. Optical bench 400also includes an underfill material 420 between active circuit 410 andpassivation layer 8 to help increase mechanical strength of opticalbench 400 in comparison to structures which do not include underfillmaterial 420. An optically transparent material 430 is between laserdiode 1 and waveguide 19.

Optically transparent material 430 helps to increase an amount of lightpropagated between laser diode 1 and photodetector 2 by reducing lightscattering, and reflection at an interface of laser diode 1 and asurrounding environment. Optically transparent material 430 increases anamount of light propagated between laser diode 1 and photodetector 2 dueto refractive index matching. That is, a difference in a refractiveindex at an output of laser diode 1 and optically transparent material430 is less than a difference in the refractive index at the output ofthe laser diode and the surrounding environment. In some embodiments,optically transparent material 430 comprises spin-on glass, an organicmaterial, a polymer material, or another suitable material.

Trench 21 includes two sloped sides. In some embodiments, a side betweenactive circuit 410 and laser diode 1 is substantially perpendicular to atop surface of substrate 3. In some embodiments, reflector layer 5extends between a bottom surface of waveguide 19 and substrate 3. Insome embodiments, reflector layer 5 is located only on the sloped sideof trench 21.

Optical bench 400 includes a single active circuit 410 connected tolaser diode 1. In some embodiments, optical bench 400 includes multipleactive circuits 410 connected to laser diode 1. In some embodimentshaving multiple active circuits 410, laser diode is selectivelyconnected to each of the active circuits 410. In some embodiments, acontrol system is configured to control which of the multiple activecircuits 410 are connected to laser diode 1 at any particular time. Insome embodiments, at least one active circuit 410 is selectivelyconnected to laser diode 1 by a TSV, such as TSV 14.

Optical bench 400 includes laser diode 1 in trench 21. In someembodiments, photodetector 2 is located in trench 21 and laser diode 1is located outside of the trench. In some embodiments, photodetector 2is electrically connected to one or more active circuits similar toactive circuit 410. Photodetector 2 is configured to convert a receivedoptical signal from laser diode 1 into an electrical signal. Thiselectrical signal is then provided to the at least one active circuitconnected to photodetector 2. In some embodiments where multiple activecircuits are connected to photodetector 2, a control system isconfigured to selectively determine which of the active circuits areconnected to the photodetector at any one time. In some embodiments, thecontrol system for controlling connections between active circuits 410and laser diode 1 is a same control system as that for controllingconnections between active circuits and photodetector 2. In someembodiments, the control system for controlling connections betweenactive circuits 410 and laser diode 1 is different from the controlsystem for controlling connections between active circuits andphotodetector 2.

In some embodiments, both laser diode 1 and photodetector 2 are locatedwithin trench 21. In embodiments where both laser diode 1 andphotodetector 2 are located within trench 21, waveguide 19 and opticallytransparent material 430 are between the laser diode and thephotodetector. In some embodiments where both laser diode 1 andphotodetector 2 are located within trench 21, the trench has no slopedsides or reflector layer 5 is omitted.

In some embodiments, optical bench 400 is formed in a manner similar tothat described in FIGS. 2A-2E or in FIGS. 3A-3C. In comparison with themethod of making described in FIGS. 2A-2E and FIGS. 3A-3C, optical bench400 includes bonding laser diode 1 in trench 21 sequentially withforming waveguide 19. In some embodiments, waveguide 19 is formed intrench 21 prior to bonding of laser diode 1 in trench 21. In someembodiments, waveguide 19 is formed in trench after bonding of laserdiode 1 in trench. In some embodiments, at least a part of waveguide 19is formed in trench 21 simultaneously with boding laser diode 1 intrench 21. Following bonding laser diode 1 and waveguide 19 in trench21, optically transparent material 430 is deposited around waveguide 19.In some embodiments, optically transparent material 430 is depositedusing a spin-on process, a PVD process or a CVD process. In someembodiments, a material removal step, such as etching, is used to removeoptically transparent material 430 from undesired locations followingthe deposition step. In some embodiments where photodetector 2 is intrench 21, the photodetector is bonded in the trench sequentially withformation of waveguide 19 in the trench. In some embodiments wherephotodetector 2 is in trench 21, the photodetector is bonded in thetrench simultaneously with formation of at least a part of waveguide 19in the trench. In some embodiments where both photodetector 2 and laserdiode 1 are in trench 21, the photodetector is bonded in the trenchsequentially with the laser diode. In some embodiments where bothphotodetector 2 and laser diode 1 are in trench 21, the photodetector isbonded in the trench simultaneously with the laser diode.

One aspect of this description relates to a first embodiment of anoptical bench. The optical bench includes a substrate having a trenchtherein with a reflective coating formed on an angled sidewall of thetrench. The optical bench also includes a first device positioned withinthe trench, a second device optically connected to the first device, atleast one an active circuit electrically connected to the first device.In addition to the first device, the optical bench includes a waveguidein the trench with the waveguide being positioned optically between thefirst device and the reflective coating. The optical bench also includesan optically transparent material that forms a first interface with thefirst device and a second interface with a first surface of thewaveguide.

Another aspect of this description relates to another embodiment of anoptical bench. The optical bench has a substrate in which a trench isformed with a reflective coating provided over an angled sidewall of thetrench. The optical bench also includes a light emitting device withinthe trench, a light receiving device optically connected to the lightemitting device, and at least one active circuit electrically connectedto the light emitting device. In addition to the light emitting device,the optical bench includes a waveguide positioned in the trench andpositioned optically between the light emitting device and thereflective coating. The optical bench also includes an opticallytransparent material that forms a first interface with the lightemitting device and a second interface with a first surface of thewaveguide.

Still another aspect of this description relates to another embodimentof an optical bench. The optical bench includes a substrate that has atrench that includes a first angled sidewall having a first slope angleand a reflective coating on the angled sidewall. The optical bench alsoincludes a light receiving device provided within the trench and a lightemitting device optically connected to the light receiving device andelectrically connected to a transmitting circuit. The optical bench alsoincludes a waveguide provided in the trench and positioned opticallybetween the light receiving device and the reflective coating. Theoptical bench also includes an optically transparent material that formsan interface with the light receiving device and an interface with afirst surface of the waveguide.

It will be readily seen by one of ordinary skill in the art that thedisclosed embodiments fulfill one or more of the advantages set forthabove. After reading the foregoing specification, one of ordinary skillwill be able to affect various changes, substitutions of equivalents andvarious other embodiments as broadly disclosed herein. Although featuresof various embodiments are expressed in certain combinations among theclaims, it is contemplated that these features can be arranged in anycombination and order. It is therefore intended that the protectiongranted hereon be limited only by the definition contained in theappended claims and equivalents thereof.

What is claimed is:
 1. An optical bench comprising: a substrate having atrench therein; a reflective coating over an angled sidewall of thetrench; a first device within the trench; a second device opticallyconnected to the first device by an optical path; at least one activecircuit electrically connected to the first device; a waveguide in thetrench, wherein the waveguide is optically between, along the opticalpath, the first device and the reflective coating; and an opticallytransparent material, the optically transparent material forming a firstoptical interface with the first device and a second optical interfacewith a first surface of the waveguide, wherein at least one surface ofthe first device is free from physical contact with the opticallytransparent material, and an entirety of the waveguide is covered by theoptically transparent material.
 2. The optical bench according to claim1, wherein: the optically transparent material forms a third interfacewith a second surface of the waveguide.
 3. The optical bench accordingto claim 2, wherein: the optically transparent material forms a fourthinterface with a first surface of the reflective coating.
 4. The opticalbench according to claim 1, wherein: the second device is above theangled sidewall of the trench.
 5. The optical bench according to claim1, wherein: the waveguide comprises: a first cladding material having afirst refractive index, and a core material having a second refractiveindex, wherein the second refractive index is at least 0.02 greater thanthe first refractive index.
 6. The optical bench according to claim 5,wherein: the waveguide further comprises a second cladding materialhaving a third refractive index, wherein the second refractive index isat least 0.02 greater than the third refractive index.
 7. The opticalbench according to claim 1, wherein: the waveguide comprises an opticalfiber wherein a first cladding material having a first refractive indexsurrounds a core material having a second refractive index, and thesecond refractive index is at least 0.02 greater than the firstrefractive index.
 8. The optical bench according to claim 1, wherein:the angled sidewall of the trench has a slope angle Θ of between about42° and about 48°.
 9. The optical bench according to claim 1, wherein:the reflective coating comprises an adhesion layer over the angledsidewall, a barrier layer over the adhesion layer, and a reflectivemetal layer over the barrier layer.
 10. The optical bench according toclaim 1, wherein: the reflective coating has a reflectivity of at least90%.
 11. An optical bench comprising: a substrate having a trenchtherein; a reflective coating over an angled sidewall of the trench; alight emitting device within the trench; a light receiving deviceoptically connected to the light emitting device by an optical path; atleast one active circuit electrically connected to the light emittingdevice; a waveguide in the trench, wherein the waveguide is opticallybetween, along the optical path, the light emitting device and thereflective coating; and an optically transparent material, the opticallytransparent material forming a first optical interface with the lightemitting device and a second optical interface with a first surface ofthe waveguide, wherein the light receiving device is free fromphysically contacting the optically transparent material.
 12. Theoptical bench according to claim 11, further comprising: a plurality ofactive circuits, each active circuit of the plurality of active circuitsbeing electrically connectable to the light emitting device; and acontrol system for selectively connecting at least one of the activecircuits to the light emitting device.
 13. The optical bench accordingto claim 11, wherein: the reflective coating extends under a firstportion of the waveguide.
 14. The optical bench according to claim 11,wherein: the optically transparent material comprises a spin-on glass(SOG), an organic material, or a polymeric material.
 15. The opticalbench according to claim 11, wherein: the light emitting device has afirst refractive index at an output surface; the optically transparentmaterial has second refractive index; and a surrounding environment hasa third refractive index, wherein a difference between the firstrefractive index and the second refractive index is less than adifference between the first refractive index and the third refractiveindex.
 16. The optical bench according to claim 11, wherein: the atleast one active circuit is electrically connected to the light emittingdevice by a through silicon via (TSV) structure.
 17. An optical benchcomprising: a substrate having a trench therein; a reflective coatingover a first angled sidewall of the trench, the first angled sidewallhaving a first slope angle; a light receiving device within the trench;a light emitting device optically connected to the light receivingdevice by an optical path; at least one transmitting circuitelectrically connected to the light receiving device; a waveguide in thetrench, wherein the waveguide is optically between, along the opticalpath, the light receiving device and the reflective coating; and anoptically transparent material, the optically transparent materialforming a first optical interface with the light receiving device and asecond optical interface with a first surface of the waveguide, whereinat least one surface of the light receiving device is free fromphysically contacting the optically transparent material.
 18. Theoptical bench according to claim 17, further comprising: a second angledsidewall having a second slope angle, wherein the first slope angle isless than the second slope angle.
 19. The optical bench according toclaim 17, further comprising: at least one receiving circuitelectrically connected to the light receiving device.
 20. The opticalbench according to claim 17, further comprising: a plurality oftransmitting circuits, each of the transmitting circuits beingelectrically connectable to the light emitting device; a plurality ofreceiving circuits, each of the receiving circuits being electricallyconnectable to the light receiving device; and a control systemconfigured for selectively connecting at least one of transmittingcircuit of the plurality of transmitting circuits to the light emittingdevice and selectively connecting at least one receiving circuit of theplurality of receiving circuits to the light receiving device.